From When Must a Bride Begin Covering Her Hair?
As is well known, a married woman is required to cover her hair. There is some question, however, as to when exactly this obligation begins. There are essentially three different opinions on the matter.
According to some authorities, a woman must begin covering her hair from "erusin,” the point at which she is formally betrothed -- though not officially married -- to her groom. According to this approach, a bride would be required to have her hair covered before the chuppa ceremony in order to ensure that it is covered once the ring is placed on her finger, at which time the erusin is completed. This opinion is actually the most difficult to justify or support, as the Talmud explicitly rules that a betrothed woman may leave her hair exposed. Some explain that the Talmudic dispensation for betrothed women to leave their hair exposed applied only in those days when the custom was that the erusin and chuppa ceremonies were held on separate occasions, sometimes as much as a year apart. In our day, however, when the erusin takes place concurrently with the chuppa ceremony, this dispensation would not apply. There are additional explanations on how to understand and rationalize this seemingly overly stringent opinion, as well.
According to other authorities, a bride’s obligation to cover her hair begins after the “nesuin” component of the ceremony which is when the couple is officially married. There is much discussion, however, as to what exactly constitutes nesuin, and by extension, when the couple is truly deemed to be married. According to some authorities, nesuin is the result of, or at least completed with, the chuppa ceremony. According to this approach, a woman would have to cover her hair before going to the chuppa since she is considered to be a nesua immediately upon conclusion of the chuppa ceremony. Furthermore, it is unanimous that once yichud has taken place, the seclusion of the bride and groom after the ceremony, the nesuin is complete. This is true whether or not marital relations have taken place. According to this approach, a bride would be required to emerge from the yichud room with her hair properly covered. The Jerusalem Talmud seems to support the view that a woman must begin covering her hair once the nesuin is completed.
According to yet other authorities, the obligation for a bride to cover her hair begins only the next morning, after marital relations are assumed to have taken place. As Rabbi Eliyahu Falk writes, “…it is known that today the custom among many orthodox Jews in America is to be lenient in this matter, and I have heard reliable testimony that this was the custom in Ashkenaz – at least in Hamburg -- and in Hungary… Even the most orthodox and daughters of great rabbis stood under the chuppa with their hair uncovered.”
So too, Rav Moshe Feinstein writes that “…the obligation to begin covering her hair only begins after the first night has passed as it is only from then that it is assumed that she is no longer a virgin. The obligation does not begin after the chuppa or the yichud as it is assumed that she is still a virgin… The requirement for her to cover her hair is dependent solely on whether she is a virgin or not, as it is written in the Mishna in Ketubot 15b… We see from here that the obligation only begins when it can be assumed that she is no longer a virgin, and this begins after the first night of marriage has passed.” Rav Shlomo Zalman Auerbach writes that “I have heard that brides are lenient with the matter of covering their hair [and don’t cover it until the next morning] and they have authorities upon who to rely…”
According to this approach, since the obligation for a married woman to cover her hair is derived from the episode of the Sotah, where it says that the Kohen would "…uncover the woman’s head” it is reasonable to assume that only a woman who is eligible to undergo the Sotah procedure is required to cover her hair. A woman, who for whatever reason never had intimate relations with her husband, is ineligible to undergo the Sotah procedure even if she is suspected of having intimate relations with another man. It is argued, therefore, that such a woman need not cover her hair, either. Similarly, since nowadays a bride and groom do not engage in intimate relations in the yichud room, there is less reason to require a bride to have her hair covered when she emerges from the yichud room.
There is also reason to suggest that the headpiece that brides customarily wear as part of their bridal outfit qualifies as an adequate head covering, at least until the next morning. This is especially true if it covers the majority of her head. According to this approach, since the bride is already wearing her head piece before the chuppa ceremony, she is essentially complying with the most stringent view, as her head is indeed covered when the erusin is completed! It is interesting to note that in the Sefardic tradition, yichud only takes place at the conclusion of the wedding meal. As such, there are additional grounds for Sefardic women to delay covering their hair until the next morning.
 Ketubot 72a.
 Mahari Halevi 9; Kinyan Torah 2:43; Az Nidberu 8:65, 12:50:1; Yechave Daat 5:62; Shevet Halevi 9:259; Teshuvot V’hanhagot 4:294; Avnei Yashfei 3:107:2; Shraga Hameir 8:24; Beit Meir, EH 21; Mishna Berura 75:11.
 Ketubot 15b.
 Shraga Hameir 8:24.
 Teshuvot V’hanhagot 4:294.
 Shevut Yaakov 1:103; Sova Semachot 1:13:1-2; Otzar Haposkim 21:27:2. See also Shita Mekubetzet to Ketubot 15b.
 Ketubot 2:1.
 Bnei Banim 3:23; Teshuvot V’hanhagot 4:294; Chatam Sofer, YD 195; Rivevot Ephraim 6 p. 570. This is also the view of Rav Yisroel Belskey, Rav Moshe Feinstein, and Rav Yakov Kaminetzky and is the widespread practice in most communities, especially in North America.
 Levusha Shel Torah 27:6.
A currently unpublished responsa that is in my possession.
 Ishei Yisrael 55, note 77.
 Bamidbar 5:18.
 Sotah 24b.
 Mahari Halevi 9. See also Shevet Halevi 9:259.